状态模式在Golang中的实现与应用详解

type OrderState interface {
    Pay(order *Order) string
    Ship(order *Order) string
    Complete(order *Order) string
}

type UnpaidState struct{}

func (s *UnpaidState) Pay(order *Order) string {
    order.state = &PaidState{}
    return "订单已支付"
}

func (s *UnpaidState) Ship(order *Order) string {
    return "无法发货，订单未支付"
}

func (s *UnpaidState) Complete(order *Order) string {
    return "无法完成，订单未支付"
}

type PaidState struct{}

func (s *PaidState) Pay(order *Order) string {
    return "订单已支付，请勿重复操作"
}

func (s *PaidState) Ship(order *Order) string {
    order.state = &ShippedState{}
    return "订单已发货"
}

func (s *PaidState) Complete(order *Order) string {
    return "无法完成，尚未发货"
}

type Order struct {
    state OrderState
}

func NewOrder() *Order {
    return &Order{state: &UnpaidState{}}
}

func (o *Order) Pay() string {
    return o.state.Pay(o)
}

func (o *Order) Ship() string {
    return o.state.Ship(o)
}

func (o *Order) Complete() string {
    return o.state.Complete(o)
}

order := NewOrder()
fmt.Println(order.Pay())     // 输出：订单已支付
fmt.Println(order.Ship())    // 输出：订单已发货
fmt.Println(order.Complete()) // 输出：订单已完成